Re: [Qemu-devel] [RFC v4 09/27] monitor: create monitor dedicate iothread

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Dr. David Alan Gilbert (dgilbert@redhat.com) wrote:
> * Peter Xu (peterx@redhat.com) wrote:
> > Create one IOThread for the monitors, prepared to handle all the
> > input/output IOs using existing iothread framework.
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  monitor.c | 29 +++++++++++++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> > 
> > diff --git a/monitor.c b/monitor.c
> > index a70ab5606b..4ce9828fab 100644
> > --- a/monitor.c
> > +++ b/monitor.c
> > @@ -76,6 +76,7 @@
> >  #include "qmp-introspect.h"
> >  #include "sysemu/qtest.h"
> >  #include "sysemu/cpus.h"
> > +#include "sysemu/iothread.h"
> >  #include "qemu/cutils.h"
> >  #include "qapi/qmp/dispatch.h"
> >  
> > @@ -208,6 +209,12 @@ struct Monitor {
> >      QTAILQ_ENTRY(Monitor) entry;
> >  };
> >  
> > +struct MonitorGlobal {
> > +    IOThread *mon_iothread;
> > +};
> > +
> > +static struct MonitorGlobal mon_global;
> > +
> >  /* QMP checker flags */
> >  #define QMP_ACCEPT_UNKNOWNS 1
> >  
> > @@ -4034,12 +4041,24 @@ static void sortcmdlist(void)
> >      qsort((void *)info_cmds, array_num, elem_size, compare_mon_cmd);
> >  }
> >  
> > +static GMainContext *monitor_io_context_get(void)
> > +{
> > +    return iothread_get_g_main_context(mon_global.mon_iothread);
> > +}
> > +
> > +static void monitor_iothread_init(void)
> > +{
> > +    mon_global.mon_iothread = iothread_create("monitor_iothread",
> > +                                              &error_abort);
> 
> That name is one character too long for pthread_setname_np that it
> ends up being passed too (it's 16 char including the terminator);
> that probably means the thread ends up unnamed.  I suggest
> you make it "mon_iothread"
> 
> > +}
> > +
> >  void monitor_init_globals(void)
> >  {
> >      monitor_init_qmp_commands();
> >      monitor_qapi_event_init();
> >      sortcmdlist();
> >      qemu_mutex_init(&monitor_lock);
> > +    monitor_iothread_init();
> >  }
> >  
> >  /* These functions just adapt the readline interface in a typesafe way.  We
> > @@ -4117,6 +4136,13 @@ void monitor_cleanup(void)
> >  {
> >      Monitor *mon, *next;
> >  
> > +    /*
> > +     * We need to explicitly stop the iothread (but not destroy it),
> > +     * cleanup the monitor resources, then destroy the iothread.  See
> > +     * again on the glib bug mentioned in 2b316774f6 for a reason.
> 
> I wonder if that bug is still live?   2b316774f6 says that:
>    'glib developers found and fixed the deadlock as part of implementing
> child sources.'
>    but doesn't say which glib version that was fixed in; we have
> increased the minimum glib version we support since 2013, so maybe...

Paolo says it wasn't fixed until 2.28 and we still allow 2.22 ; so a
little way before we can declare that one dead.

Dave

> Dave
> 
> > +     */
> > +    iothread_stop(mon_global.mon_iothread);
> > +
> >      qemu_mutex_lock(&monitor_lock);
> >      QTAILQ_FOREACH_SAFE(mon, &mon_list, entry, next) {
> >          QTAILQ_REMOVE(&mon_list, mon, entry);
> > @@ -4124,6 +4150,9 @@ void monitor_cleanup(void)
> >          g_free(mon);
> >      }
> >      qemu_mutex_unlock(&monitor_lock);
> > +
> > +    iothread_destroy(mon_global.mon_iothread);
> > +    mon_global.mon_iothread = NULL;
> >  }
> >  
> >  QemuOptsList qemu_mon_opts = {
> > -- 
> > 2.13.6
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK